The Bangkok shutdown began ahead of schedule on Sunday evening, with roadblocks being set up at several key intersections and anti-government protesters beginning to trickle to the sites. On the social media, it already warranted its own hash tag.

Overnight, elaborate stages, sound systems, generators, kitchens and toilet trucks were set up by the clearly well-funded People’s Democratic Reform Committee (PDRC) led by the southern politician Suthep Thaugsuban.

By around 8am on Monday, sprawling camps had been established for the thousands who gathered, with tents spread across roads and over pavements. And street vendors were out in full force selling the paraphernalia of protest – Thai flags, ribbons, whistles – the signature of the self-styled “people’s revolution” - and T-shirts commemorating the “Bangkok shutdown”.

Those caught unawares in cars on Sunday evening were ensnared in traffic jams.

But there were no jams on Monday morning; maps of the protest zones had been published by the media, and most people knew which areas to avoid – or if their offices were in the affected zones they simply stayed at home.

“Attendance is 80 per cent down,” a manager of an investment company said on the phone from his office on Sathon road in the business district.

As a result, streets around the protest sites were eerily empty – though the BTS “Skytrain” and underground MRT lines ran unaffected – and were packed with people.

The rally sites on lower Sukhumvit closed down most of the access to the upscale retail and business districts of downtown Bangkok, with travel possible only on the ubiquitous motorcycle taxis or on the trains.

Shops on the route were mostly shuttered. Possibly because of the dense crowds using smartphones and tablets, Internet connection at the rally sites slowed to a crawl.

Through the morning, speeches and music boomed from the gigantic sound systems. The outer periphery of each rally site was manned by men at barriers – the security “guards” who have been taking bullets from sporadic drive-by shootings at night.

This is the typical low-level violence that one has seen at these prolonged protests – carrying on for days and weeks and if no political exit presents itself, carrying the potential of finally exploding in major violence as in 2008, 2009 and 2010.

The government has been on the back foot for weeks, wary of being accused of using violence. Eight people have died and scores have been injured so far in the three months of protests aimed at forcing the Yingluck Shinawatra government out of office. The PDRC and its supporters including the opposition Democrat Party whose leader Abhisit Vejjajiva was also appearing at the rallies, see the Yingluck government as a puppet and pawn of the premier’s older brother, the billionaire Thaksin Shinawatra, in self-exile abroad dodging a two year sentence for corruption.

Police presence at the rallies was negligible. The close to 20,000 police and troops were largely, it seems, deployed to protect government buildings, which saw a few hundred protesters blocking them. By mid afternoon the Ministry of Foreign Affairs had to abandon its building and shift to the Queen Sirikit National Convention Centre.

The police has deployed just over 10,000 officers armed mostly with just shields, batons and riot control gear – not with guns. The 8,000 or so military troops deployed are also unarmed. In the afternoon, army spokesman Colonel Winthai Suwari left little doubt as to where the military’s sympathies lie when he said the army units had been deployed to protect the protesters from any attempt by the government to harm them.

Most Thais and analysts believe a military coup is inevitable and could come this week if the protests drag on, become more aggressive, or there is an outbreak of violence. The army is known to be reluctant to put men and tanks on the street in an overt takeover, however – because it is mindful of an international backlash and worse, a backlash from the well organised ‘’red shirt’’ movement that has backed Thaksin and helped propel Yingluck to power in the 2011 election.

What form the intervention may take is a subject of much speculation. The army has launched as many as 18 successful or attempted coups since Thailand became a democracy – under a constitutional monarchy – in 1932.